1. Field of the Invention
This invention generally relates to electric discharge lamps and has particular reference to an improved fluorescent lamp of compact size and high brightness that has a partitioned envelope and is suitable for use in residential and commercial lighting fixtures.
2. Description of the Prior Art
Electric discharge lamps having envelopes which are internally partitioned to provide one or more elongated discharge paths are generally well known in the art. U.S. Pat. No. 2,121,333 to Barclay discloses a single-ended type lamp of such construction wherein glass panels joined to the glass envelope serve as the partition means. Another fluorescent lamp of this type is disclosed in U.S. Pat. No. 3,024,383 to Doering and employs a thin sheet of glass or suitable ceramic as the partitioning means which divides the interior of the envelope into either two or four interconnected sectors. A double-ended fluorescent lamp having a longitudinal partition that extends along the axis of a tubular envelope between two pairs of oppositely-disposed electrodes to provide a dual-arc device is disclosed in U.S. Pat. No. 3,084,271 to C. E. Swanson.
Discharge lamps having tubular envelopes with partition means or a filler, such as a core member, that prevent the arc from passing along the axis of the lamp between electrodes located at the ends of the envelope are also generally well known in the art. U.S. Pat. No. 1,963,962 to Barclay, for example, discloses a discharge lamp having a tubular envelope that is partitioned in such a manner that a plurality of arc channels are provided which are disposed around a central bore or chamber. U.S. Pat. No. 2,133,205 to McCauley discloses a tubular double-ended discharge lamp that has a channeled core or filler member which forces the arc to follow various paths around the core member and produce a changing luminous effect.
Various other types of fluorescent lamps having envelopes that are so constructed that the discharge is prevented from passing along the center of the envelope (or is forced to follow a path confined to a space around an inner envelope component) are disclosed in U.S. Pat. Nos. 3,521,120 (Anderson); 3,953,761 (LoGiudice, FIGS. 6-8 embodiments); and 4,095,135 (Yamazaki et al.). A fluorescent lamp having a bulb which forces the arc to follow a helical path around the lamp axis is disclosed in U.S. Pat. No. 3,899,712 to Witting. Another fluorescent lamp of helical-arc design having a tubular envelope which contains a coaxial closed tube that houses lead-in conductors and thus permits the electrodes to be disposed at opposite ends of the envelope with all of the lead-in conductors extending through the same end of the envelope so that the lamp is of single-ended construction is disclosed in U.S. Pat. No. 3,903,447 to Young et al. A glow discharge device which also has a helical-arc channel and a centrally-chambered envelope which permits lead wires to be sealed through the same end of the envelope and connect with electrodes located at opposite ends of the envelope is disclosed in U.S. Pat. No. 2,847,603 to Engelbart.
While the prior art discharge lamps were satisfactory in the sense that they reduced the physical size of the lamp by forcing the arc to follow a tortuous path that was much longer than the axial length of the envelope, they were rather complicated and expensive to manufacture and were not very efficient. In addition, they failed to teach those skilled in the art how to construct a single-ended discharge lamp having a retroverted arc channel that forced the discharge to traverse or "pass through" the envelope an odd number of times in longitudinal fashion. The concept of an electric discharge lamp of double-ended construction having a partitioned envelope that defines a retroverted arc channel which forces the discharge to "pass through" the envelope longitudinally an even number of times is also not found in the teachings of the aforementioned prior art patents.